Process for producing olefins



July 12, 1960 w. A. PARDEE 2,945,076

PRocE-ss FOR PRoDucING oLEFINs Filed April l5; 1957 Pnocnss nonPnonUcrNc oit-arms William A. Pardee, Fox Chapel, Pa., assigner to GulfResearch & Development Company, Pittsburgh, Pa., a corporation ofDelaware Filed Apr. 15, 1957, ser. No. 652,946

s claims. (ol. 26o-m3) This application relates to a process -forproducing olens and more particularly to a process for produclng normalalpha-olens by cracking paranic stocks.

Olens, particularly normal alpha-olefins, are often extremely desirablefor use in many chemical reactions. For example, `a convenient landextensive use for olelins resides in the Oxo process wherein they arereacted withv hydrogen and carbon 'monoxideV in the presence of acatalyst, generally cobalt carbonyl, at high pressures and moderatetemperatures to produce a product predominating in aldehydes having onemore carbon atom than said olens. The aldehydes produced are often, inturn, hydrogenated to the corresponding alcohols. Since primary straightchain aldehydes and, particularly, the corresponding alcohols areextremely valuable commercially, it is apparent that normalalpha-olelins would be considered attractive as charge stock in the Oxoprocess.

In accordance with the present invention, paralnic hydrocarbons such aspetroleum waxes, are subjected to well-defined cracking and recoveryoperations wherein a large conversion of said hydrocarbons to a productpredominating in normal alpha-olens is obtained. At the same time,secondary reactions likely to result in the production of undesirablediolefns `and isomerization, polymerization, decomposition, etc.,products are inhibited.

As an illustration of but one embodiment of my invention, -a :Elowdiagram of the present process is shown in Figures 1, 2 and 3 of thedrawings, which drawings Iare hereby incorporated in and made part ofthe present application.

A parainic charge stock is introduced into the system by line 2,preferably in the molten state at a temperature of about 200 to about300 F. Prior to its introduction into the cracking zone, the charge canbe joined by a recycle stream, described and dened hereinafter, in line.4. In order to vaporze the combined charge in line 6, Water isintroduced in the system by line 8 and convertedv to steam in heater 9by any convenient means, for example by gas burners, not shown, to atemperature of about 900 to about 1200 F. The temperature of the Vsteamshould be high enough to vaporize kthe combined charge from line 6 butlow enough to prevent appreciable cracking thereof before its entry intothe cracking zone. The pressure of the charge in line 6 and of the steamproduced in line 3, though not critical, should be suiicient to overcomepressure drop through the system. I have found that a pressure betweenabout 15 to about 40 pounds per square inch gauge is sucient for suchpurpose. In order to obtain efficient and optimum vaporization of thecharge stock and to control the contact time of the charge stock in thecracking chamber, the ratio of 'steam to charge stock is extremelyimportant. In general at least about 2 percent byweight, and preferably-about 3 to about 40 percent by weight, of steam, based upon the totalcharge stock, is suicient to vaporize the charge stock satisfactorilyand maintain the desired contact time. As charge stock any paraiinichydrocarbon v asume Patented July 12, 1960 such as wax, natural as wellas synthetic, is suitable, although a petroleum wax is preferred. It is`further preferable that the wax be substantially free of oil. Whilewaxy materials containing up to about 41 percent by weight of oil havebeen used successfully, a preferred charge would contain less than about16 percent by weight of oil. Best results are obtained using petroleumparaflfins having a melting point of about 130 to about 140 F. and anoil content of less than about one percent by Weight.

The molten charge stock and steam are combined in linelt) and passedthrough cracking chamber 12 wherein the vaporized charge stock iscracked and a hydrocarbon mixture predominating in C2 to C20 oleiins, inthe present example, is obtained. In order to obtain satisfactorycracking in chamber 12, careful control of the reaction conditionstherein is required. The temperature must be at least about 1000 F. inorder to crack the charge stock at a reasonable rate, but should bemaintained below about l250 F. in order to inhibit secondary reactionsand prevent excessive coking in chamber 12. Preferably a temperature ofabout 1000 to about 1175 F. and a pressure of 4about one to about threeatmospheres is extremely satisfactory. The residence time is similarlyextremely important in order to obtain satisfactory cracking and inhibitsecondary reactions. In general a residence time, dependent, of course,upon the remaining variables, is about 0.2 to about 6.0 seconds,particularly about 0.5 to about 3.0 seconds.

The mixture of cracked products and steam removed from cracking chamber12 is passed to flash tower 14 by line I3. Before this mixture is passedinto flash tower I4, it is quickly cooled from cracking temperature to atemperature of about 600 to about 800 F., preferably to a temperature ofabout 675 to about 725 F. to forestall further-cracking and/or secondaryreactions. This time interval is extremely important and must be lessthan about 2 to about 3 seconds, preferably between about 0.02 to about0.10 second. The cooling is effected by a recycle stream from line 16,the composition of which will be defined hereinafter. The purpose ofiash tower 14, which is operated at a pressure of about 10 to about 30pounds per square inch gauge and a temperature of about 600 to about 700F., is to effect a separation of the steam and lighter products from theheavier liquid products produced in the cracking operation. Moreoversuicient recycle of heavier product is thus provided to cool the crackedproduct before its entry into flash tower 14. A mere separation ofsteam, as condensed water, from the total cracked products would beexceedingly di'icult because of a tendency to form an emulsiontherewith.

Under the pressure and temperature conditions existing in flash tower14, set `forth above, the products removed from the top of the towerthrough line 18 co1nprise C12 to C20 and lighter hydrocarbons,preferably C16 to C18 and lighter hydrocarbons, and water as steam. The`products `are then passed through cooler 20 wherein the steam iscondensed .to water. The .temperature in cooler20 is not critical aslong as it is suciently low to condensethe steam ther-ein but not so lowas to effect precipitation or crystallization of waxy materials whichmay be present in the stream due to incomplete separation in ash tower14. In .gener-al a temperature of about to about 125 F.,preferably'about 100 F., is satisfactory. In addition to water, some of`the heavier cracked products .are also condensed in cooler 20. Thecooled product is removed lfrom cooler 20 by line 22 and passed .toseparator 24 which is operated at a temperature of .about to about 125F. and a pressure of about 8 to about 12 pounds per square inch gauge.The water is removed from the base of separator 24 by line 26, whileCglto C6 and lighter cracked products,

3 preferably C5 and lighter, are removed overhead by line 28.. Theremainder of the cracked products are removed from the side of separator214 by line 30.

From the base of ash Ytower 14, through line 32, is removed theremainder of the product which may not have been removed overhead byline 18', that is about YC12 to `about C20 and heavier, preferably aboutC10 to about C12 and heavier hydrocarbons. Since it is necessary to coolthe cracked products entering flash tower 14, as previously pointedout,V and since it is extremely desirable to eect such cooling withoutresorting to the addition to the system of extraneous material whichwould subsequently have to be removed from the product, if not from thesystem, often at .great trouble and expense, -a portion of the productin line 32 is recycled` by line '34, and passed through cooler 35wherein therproduct is cooled toa temperature of about 300 to about 500preferably C11 to `C10 and lighter hydrocarbons while the fractionremoved from the base of fractionator 64 by line 4 comprises C12 `to C20and heavier hydrocarbons, preferably C11 to C10` and heavierhydrocarbons. rlhe bottom fraction is preferably recycled and joins thefresh charge i-n line 2 as previously described. This recycle comprisesabout 100 to .about'300 percent by weight, based on the fresh charge inline 2. In the event, however, operation isV such, dor example, thatline 18 contains all or substantially all of the C .and lighterhydrocarbons in Ithe cracked product and C1, and heavier hydrocarbonsare to be used as recycle of line 4, the overhead fromvtar stripper 46need not be sent to frac- Y `tionator 64 but can be passed directly toline 4 for F. The cooled product is then introduced into line 13 by line16. The amount of recycle depends on many variables, for example, itstemperature, the temperature of the cracked product in line 13, thetemperature desired in ilash tower 14, etc. In general, atleast about100, and preferably about 150 to about 300 percent, by Weight ofrecycle, based on the cracked product in line 13, is suicient to effectthe desired cooling.

The remainder of the heavier product is passed by line 36 through valvev3&8 wherein the pressure is reduced to about 3 to rabout 8 pounds persquare inch gauge, preferably to about atmospheric pressure. The productat a reduced pressure and at a somewhat reduced temperature, because ofits movement through lines 36 and 40 and its reduction in pressure inpassing through valve 38, is heated, if necessary, in heater 42 by anyconvenient means, to a temperature of about the same order )as thatexisting in flash tower 14.

The product leaving heater 42 by way of line 44 is passed to tarstripper 46 wherein tar and other. similar .products present in thebottoms product are removed therefrom. This is effected by passing about40 to about 70 pounds` of steam per barrel of product in line 44, at atemperature of about 600 to about 800 F. into the base of tar stripper46 by line 48. A Vtemperature of about 600 to about 800 F. and apressure of about 2 .to .about 6 pounds per square inch gauge isemployed therein. As a result thereof, tar :and heavier coke-formingproducts'are removed `from the base of tar stripper 46 by line 50.

Removed overhead by line 51 are the remainder of the cracked productsenter-ing .tar stripper, not removed by line `50, and steam. The mixturein line 51 is then passed through cooler 52, which is operated at aternperature suiliciently low to condense the steam and some of thecracked products but not so low as to elect precipitation orcrystallization of waxy materials which may be present in the stre-amdue to incomplete separation in tar stripper e6 or llash tower 14.Generally a .temperature of about 75 .to about 125 F. is suflicient. Thecooled product is removed from cooler 52 by line 54 and passed toseparator 56 which is operated at a temperature or" about 100 to about125 F. and a pressure Yof about 0 to about 5 pounds per square inchgauge.

Water which is condensed is removed from the base of separator 56 byline 53 and C0 to about C0 hydrocarbons, .preferably about C1 to aboutC5 hydrocarbons are removed overhead by line 60. The remainder of theYcracked product which has been liqueed is removed from theseparator 56by line 61 and is preferably pressured by pump 62 to a pressure of about15 to about 25 pounds per square inch gauge. The product in line 61 isthereafter introduced into lfraction'ator 64, which is maintained at areboiler temperature of about 400 to about n 700 F. anda pressure ofabout 25toabout 5 pounds per square inch gauge, wherein the product isseparated 'into two fractions. The overhead, which is lremoved by line66, comprises C12 to C20 and lighter hydrocarbons,

recycle.

As shown in Figure 1, the olens produced are recovered and found `inlines 23, 60 and 66. The recovery of the oleiins inthese lines intotheir individual components, or even combinations or fractions of olens,can be eected in any desiredmanner. For example, in the event theoleiins in lines 28 and 60 comprise C2, C2 and *C1 oleiins, they can becombined, as shown in Figure 2, in line 68, compressed, dried byconventional Ymeans (not shown) and passed to fractionator 70 which canbe operated at a pressure of `about 250 to about 400 pounds per squareinch gauge and an overhead temperature of about 0 to about 5 F. Methaneand `any other lighter constituents which may be present, are removedoverhead by line '72, while C2, Cavand C4 hydrocarbons are removed Vfromthe base of fractionator 70 by line 74. From line 74, the C2, C3 and C1fraction is passed to fractionator 76 which is operated at a' pressureof `about 250 to about 350 pounds per square inch gauge and an overheadtemperature of abouti-10 to -about -|-l0 F. Here the C2 fraction isremoved overhead by line 78 and the C3 and C4 fraction is removed `fromthe base by line 80. The C2 stream maybe split into C21-I1 `and C21-I0by means of a column operating lat about 270`pounds per square inch andan overhead temperature of labout 20 to about 23 F. The C0 and C4 streammay be further separated by similar distillation in a column (not shown)operating at about 250 pounds per square inch tand an overheadtemperature of about 110 to about 115 F.

Similarly, the hydrocarbon fraction .in line 66 can be separated intoits individual components by any conventional means. Thus as shown inFigure 3, assuming the hydrocarbon fraction in line 66 contains C15 andlighter hydrocarbons, it is sent to fractionator 82 which is operated ata pressure of about 30 to about 100 pounds per square inch and anoverhead vapor temperature of about 122 to about 212 F. C5 and lighterhydrocarbons are removed overhead by Vline 84 Aand C0 to C1,-Jhydrocarbons are removed from the base by line 86. This latter fractionis passed tofractionator 88, operated at a pressure of about l5 to about30 pounds per square inch `and `arroverhead vapor temperature of about'150 to about 190 F., where C0 fraction is removed Y lightest individualfraction Vis removed overhead and the yremainder is removed from thebase Iand passed to the next ksucceeding column, until the fractioncontaining ,C15` and higher hydrocarbons is passed by line 94 tofractionator 56, operated at a pressure of about 5 to about 50millimeters mercury absolute andan overhead vapor temperature of aboutV240" to about 350 F., wherein the C15 fraction is removed overhead inline 98 and the C10" and heavier fraction is removed from theVbasethereof byline toline 4 of Figure l.

While it has been shown `above that the hydrocarbon fraction can beseparated into its individual components,

this has been done merely for illustrative purposes, and

it is Within the scope of the present invention to separate thehydrocarbon fraction prepared in the cracking zone into fractionscontaining various numbers of individual components. Thus a C11 to C14fraction can be removed and used as such in alkylation or sulfonationreactions. Since there is a spectrum of hydrocarbons obtained in thecracking operation in accordance with this process and C2, C6 and C10hydrocarbons predominate, fractionationV can be effected to remove theseas individual components therefrom and not the others. Y

The process of the present invention can be illustrated byY thefollowing example. In -a processing period 2366 pounds of Gulf ProcessWax A, a typical regular grade parain wax for this process having thefollowing inspection:

Gravity, API 34.3 Viscosity, SUV, sec- 52.1 210 F. i Flash, P-M, F 435vPour point, F 115 ASTM D 97-47 `Oil content, percent by wt 22.4

ASTM D 721-53T Carbon residue, Conradson, percent 0.12

ASTM D 189-52 Aniline point, F 251 ASTM D6 l 1-2--5 3T was introduced inline 2 at a temperature of 300 F. and mixed with 4435 pounds of recyclein line 4. The mixture was Iadmixed with834 pounds of steam at atemperature of 1000 F. and a pressure of 28 pounds per square inch gaugefrom line 8 and the resulting mixture was introduced in cracking chamber12 which was maintained lat ya temperature of 1040 F. and a pressure ofpounds per square inch gauge. The mixture was permitted to remain in thecracking coilS seconds and then removed and cooled to a temperature of675 F. in 0.10 second by admixing therewith 20,240 pounds of recyclefrom line 16. The cooled mixture was then passed to ash tower 14,maintained lat -a temperature of 610 F. and a pressure of 15 pounds persquare inch gauge, where 32,270 cubic feet of gaseous materialcomprising 17,970 cubic feet of steam andA 14,300 cubic feet of C12 andlighter hydrocarbons were removed overhead by line 18. This mixture waspassed through cooler 20, where the temperature was reduced to 100 F.,and then to separator 24. Water was removed from the base of 'separator24 by line 26, 6970 cubic feet of C5 and lighter hydrocarbons wereremoved by line 28 and 1030 pounds of C11 to C12 liquid hydrocarbonswere removed by line 30.

Removed from the base of flash tower 14 were 25,152 pounds of C12 andheavier hydrocarbons. 20,240 pounds of this mixture were passed throughcooler 35, cooled therein to a temperature of 490 F. and passed by line16 to line 13 to cool the product therein to 675 F. The remainder of theproduct in line 32 was passed through valve 38 where the pressure wasreduced to 5 pounds per square inch gauge and thereafter to heater 42wherein the temperature thereof was raised to 600 F. From heater 42,heated mixture was led to tar stripper 46. 810 pounds of steam at 700 F.wereled into the stripper, wherein the temperature was 650 F. and thepressure 4 pounds per square inch gauge. 870 pounds of tar and similarproducts were removed from the base of tar stripper 46 by line l50 and8660 cubic feet of cracked products were removed overhead by line 51.After cooling in cooler 52 to a temperature of 100 F., the crackedproducts were passed to separator 516 wherein the water which wascondensed at the lower temperature was removed by line 58. There was anegligible amount of hydrocarbon gas to be removed overhead in line 60so that the total hydrocarbon stream comprising 4042 pounds of C12 andheavier materials was removed by line 61. The cracked f 6 products inlines 28, 60 and 61 were thereafter Vseparated into -the individualcomponents in the manner previously described. The results obtained aretabulated below'in Table I Alpha-Glenn Yield, Alpha-Olen Concen- Percentby Weight tration, Percent by of Feed Weight of Oletlns in CarbonFraction Regular Premium Regular Premium Feed Feed Feed Feed The highyields of total a-oletins from both the fregularf and the premium feedstocks and the high concentrations of the a-olen components in thevariouscarbon fractions are illustrative of the effects of rapid heat- Yup time, rapidl quench rate and short residence time in the crackingzone. 4

Obviously many modilications and variations of the invention, ashereinabove set forth, can be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim: e Y

' 1. A method yfor producing normal alpha-ole'ns `which comprisesvaporizing a waxy charge by admixing therewith at least about 2 percentby weight of steam at a temperature of about 900 to about 1200 F.,heating the resulting mixture at a temperature of about 1000 to about1250 F. and a pressure of about one to about three atmospheres for about0.2 to about 6.0 seconds, whereby the wax charge is cracked and amixture predominating in normal alpha-oleiins is produced, cooling saidlatter mixture to -a temperature of about 600 to about 800 F. in lessthan about 3 seconds, passing said cooled mixture into a ash tower,separating and removing a light hydrocarbon fraction from said ashtower,'removing the remainder of said cooled mixture from said tower,cooling and recycling a portion of the said remainder to constitute thesole means whereby the cracked products are cooled prior to their entryinto said ash tower, and thereafter separating the cracked product intoselected olefinic fractions.

2. A method for producing normal alpha-olefins which comprisesvaporizing a waxy charge by admixing therewith at least about 2 percentby weight of steam at a temperature of about 900 to about 1200 F.,heating the resulting mixture at a temperature of `about 1000 to about1250 F. and a pressure of -about one to about three atmospheres forabout y0.2 to about 6.0 seconds whereby the wax charge is cracked and amixture predominating in normal alpha-olens is produced, cooling saidlatter mixture to a temperature of about 600 to about 800 F. in lessthan about 3 seconds, passing;

said cooled :mixture into a ash tower, .separating and removing C12 toC20 and lighter hydrocarbons from said ash tower, removing the remainderof said cooled mixture from said tower, cooling a `portion of saidremainder to a temperature of about 300 to about 500" F. and recyclingsaid portion of said remainder to constitute the sole means whereby thecracked products are cooled prior to their entry into said ash tower,and thereafter separating the cracked product into selected olenicfractions. I

3. A method for producing normal alpha-oleiins which comprisesvaporizing a waxy charge by admixing therewith at least about 2 percentby weight of steam at a temperature of about 900 to about l200 F.,heating the resulting mixture at a temperature of about 1000 to about1250" F. and a pressure of about one to about three atmospheres forabout 0.2 to about 6.0 seconds, whereby the wax charge isV cracked and amixture predominating in normal valpha-ole'iins is produced, coolingsaid latter mixture to -a temperature of about 600 to about 800 F. inless than about 3 seconds, passing said cooled mixture into a flashtower, :separating and removing a mixture of C12 to C20 andl lighterhydrocarbons and steam from said ash tower, cooling said latter mixtureto condense said steam, removiugrwater condensate from said lattermixture, removing-the remainder of said cooled mixture from said tower,cooling a portion of said remainder to a'temperature of about 300 to`about 500 F., admixing with the cracked products said portion of saidcooled remainder to consti- `tute the sole means by which the crackedproducts are cooled prior to their entry into said ilash tower, andthereafter separating the cracked product into selected olelinicfractions.

4. A method for producing normal alpha-olens which comprises vaporizingVa waxy charge by admixing therewith at least about 2 percent by weightof steam at a temperature of about 900 to about 1200o F., heating theresulting mixture at a temperature of about 1000" to about l25`0 F. anda pressure of about one to about three atmospheres for about 0.2 toabout 6.0 seconds, whereby the wax charge is cracked and a mixturepredominating in normal alpha-olefins is produced, cooling said lattermixture to a temperature of about `600 to about y800 F. in less thanabout 3V seconds, passing said cooled mixture into a flash tower,separating and removing a mixture of C12 to C10 and lighter hydrocarbonsand steam from-said flash tower, cooling said latter mixture to condensesaid steam, removing vwater condensate `from said latter mixture,removing the remainder of said cooled mixture from said tower, cooling afirst portion of said remainder to a temperature of about 300 to about500 F., admixing with the cracked products said first portion of saidcooled remainder to constitute the sole means by which the crackedproducts are cooled prior to their entry into said ash tower, removingtar from a second portion of saidremainder, and thereafter separatingthe cracked product into selected olenic fractions. Y

5. A method for producing normal alpha-olens which comprises vaporizinga waxy charge by admixing therewith at least about 2 percent by weightofsteam at a temperature'of about 900 to about 1200 F., heating theresulting mixture at a temperature of about 1000 to' about 1250 F. andapressure of about one to about three atmospheres for about 0.2 to about6.0 seconds, whereby the wax charge is cracked and a mixturepredominating in normal alpha-oleiins is produced, cooling said lattermixture to a 'temperature of about v600 to about 800 F. in less thanabout 3 seconds, .passing said cooled mixture into a flash tower,separating and removing a mixture of C12 to C20 and lighter hydrocarbonsand steam-from said ilash tower, cooling said latter mixture to condensesaid steam, removing water condensate from said latter mixture, removingthe remainder of said cooled mixture from said tower, cooling a rstportion of said remainder to a temperature of about 300 F. to about 500F., admixing with the cracked products said first portion of'said cooledremainder to constitute the sole means by which the cracked products arecooled prior to their entry into said flash tower, removing tar from asecond portion of said remainder by admixing steam therewith, andthereafter separating the cracked product into selected olenicfractions.

References Cited in the iile of this patent UNITED STATES PATENTS2,172,228 Van Peski Sept. 5, 1939 12,366,521 Guichet Jan. 2, 11945I2,736,685 Wilson et al Feb. 28, 1956 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No; 2,945,076 July 12g 1960 William A.,Pardee. It is hereby certif-ied that error appears in the printedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 8, line 2 foriCl2 to C10" read C'l2 to C20 Signed and sealed this4th day of April 1961.,

(S EAL) Attest; ERNEST W. SWIDER XEXXXXIX ARTHUR w. CROCKER AttestingOicer Acting Commissioner of Patents

1. A METHOD FOR PRODUCING NORMAL ALPHA-OLEFINS WHICH COMPRISESVAPORIZING A WAXY CHARGE BY ADMIXING THEREWITH AT LEAST ABOUT 2 PERCENTBY WEIGHT OF STEAM AT A TEMPERATURE OF ABOUT 900* TO ABOUT 1200*F.,HEATING THE RESULTING MIXTURE AT A TEMPERATURE OF ABOUT 1000* TO ABOUT1250*F. AND A PRESSURE OF ABOUT ONE TO ABOUT THREE ATMOSPHERES FOR ABOUT0.2 TO ABOUT 6.0 SECONDS, WHEREBY THE WAX CHARGE IS CRACKED AND AMIXTURE PREDOMINATING IN NORMAL ALPHA-OLEFINS IS PRODUCED, COOLING SAIDLATTER MIXTURE TO A TEMPERATURE OF ABOUT 600* TO ABOUT 800*F. IN LESSTHAN ABOUT 3 SECONDS, PASSING SAID COOLED MIXTURE INTO A FLASH TOWER,SEPARATING AND REMOVING A LIGHT HYDROCARBON FRACTION FROM SAID FLASHTOWER, REMOVING THE REMAINDER OF SAID COOLED MIXTURE